It has been long known that fibers and fabrics prepared from ethylene terephthalate polymers are subject to soiling by oil-based soils. For that reason, a wide variety of soil release agents has been developed. Particularly effective soil release agents and a three step process for their preparation are disclosed by Scheibel et al. in U.S. Pat. No. 4,968,451. In a typical embodiment of the Scheibel et al. process, the first two steps involve (i) transesterification under an inert atmosphere, and (ii) oligomerization under reduced pressure, of dimethyl terephthalate, propylene glycol and an allyl ethoxylate to yield allyl end-capped propylene terephthalate polyester oligomer (and methanol and excess propylene glycol as by-products). In a third step, the allyl end-capped propylene terephthalate polyester oligomer is sulfonated with a source of bisulfite in an aqueous system in the presence of a free radical initiator.